Carbon pricing and system reliability impacts on pathways to universal electricity access in Africa

Off-grid photovoltaic systems have been proposed as a panacea for economies with poor electricity access, offering a lower-cost “leapfrog” over grid infrastructure used in higher-income economies. Previous research examining pathways to electricity access may understate the role of off-grid photovoltaics as it has not considered reliability and carbon pricing impacts. We perform high-resolution geospatial analysis on universal household electricity access in Sub-Saharan Africa that includes these aspects via least-cost pathways at different electricity demand levels. Under our “Tier 3" demand reference scenario, 24% of our study’s 470 million people obtaining electricity access by 2030 do so via off-grid photovoltaics. Including a unit cost for unmet demand of 0.50 US dollars ($)/kWh, to penalise poor system reliability increases this share to 41%. Applying a carbon price (around $80/tonne CO2-eq) increases it to 38%. Our results indicate considerable diversity in the level of policy intervention needed between countries and suggest several regions where lower levels of policy intervention may be effective.

findings and their significance.Provide recommendations for future research or policy implications.References: Ensure that all references are cited correctly and consistently throughout the manuscript.In conclusion, while the topic of the manuscript is noteworthy and relevant, it requires significant revisions to improve its overall quality.The authors should focus on enhancing the structure and coherence of the paper, providing sufficient detail in the methods section, and rephrasing the title to make it more declarative.These revisions will enhance the manuscript's readability and impact.I recommend that the authors carefully address the above-mentioned issues and consider incorporating the suggestions into their revised manuscript.

Reviewer 1
The manuscript focuses on an important aspect of providing high level of energy access in SSA: how to change the low pace of increasing access, and what are the optimal technology mixes in providing access.As the progress in increasing electrification to the population has slowed down post Covid period, the policy options to go back to the positive track becomes important.The authors use the available GIS based analytical tools in a robust way and communicate the results and the sensitivities convincingly.
We thank the reviewer for their feedback and are encouraged that they feel the results and sensitivities are communicated clearly.

2
The authors have analysed the impacts of 2 policy options on the electrification pathways: 1) applying penalties for unmet demand and 2) applying carbon pricing.
The analysis shows both have strong impacts both on the electrification rates and strong positive impact on the optimal technology mix from climate emission point of view.
The key question is what is reality in the policy agenda of applying the above mentioned policy instruments in the given timeline in the SSA development setting.This is not only a critical question as the application of these policy instruments are not uniform even in the developed economies setting (there are some well-functioning Carbon taxing i.e., Canada, Japan some European countries, and Carbon trading schemes ie. in EU), but some can argue that adding a penalty to the under-financed stateowned energy companies would simply amplify the barriers in the electrification process.
We thank the reviewer for these comments.We are pleased they were able to gain a picture of how the technology mix changes as different policy interventions are tested.We strongly agree with the reviewer that reference to real-world policies was underdeveloped in the manuscript and have made changes outlined below.
Firstly, on the point relating to the non-uniformity of policy interventions, we recognise this as an important point.In recognition of this, in our analysis, we conduct regional sensitivity to understand the level of financial support that there would need to be for impact.We have explicitly linked the point about non-uniformity directly when outlining the research questions in the final paragraph of the introduction, on Page 4: "And, finally, acknowledging the unevenness of existing policies and country heterogeneity, what is the sensitivity to different levels of policy intervention and how does this vary spatially?" We agree with the reviewer that adding a penalty for unmet demand could amplify barriers to electricity access.We now directly acknowledge this point in the discussion section on Page 13: "In practice, implementing a financial penalty for poor reliability, as is done in some high-income countries such as Norway, the Netherlands and the UK41, 42, may not be feasible or desirable in countries where electricity supply companies are in a state of financial stress." Partly in response to this point, we also outline how a performance subsidy for high-reliability systems could be applied instead, see further information below.

# Comment Response
If the authors could provide some examples in some SSA countries (or from other developing countries) where these instruments were tried or introduced, it could increase the research added value to the policy agenda and decision making as well as to the ongoing research discussion.Otherwise, the well prepared analysis has the risk of remaining only an academic exercise.
Linking to policy examples is important and this was not well developed in the previous draft.In the discussion section on Pages 13-4, we have discussed policy examples for both carbon pricing schemes, and regarding reliability interventions.
For reliability, the precedent of applying a penalty for outages in electricity supply comes from high-income countries.We have therefore detailed examples where penalties are charged to energy supply companies for power outages.Given the point raised above regarding the possible negative implications of applying a penalty scheme to cash-strapped distribution companies, we give an example from sub-Saharan Africa of a subsidy scheme paid to mini-grid operators for high-reliability systems: "In practice, implementing a financial penalty for poor reliability, as is done in some high-income countries such as Norway, the Netherlands, and the UK [41,42] may not be feasible or desirable in countries where electricity supply companies are in a state of financial stress.Instead, offering an incentive scheme such as a performance-based subsidy for supply companies offering households a higher level of reliability may be a viable alternative.This has been demonstrated in Nigeria where some mini-grid developers are paid a subsidy per connection provided a minimum level of reliability is met [12,43].Policymakers should seek to design mechanisms that can ensure reliable electricity access options are implemented and thus reduce the negative impacts felt by households from unreliable electricity grids in many SSA countries." We have included additional information in the Supplementary Materials demonstrating a way in which a reliability subsidy could be implemented that would have the same impact as applying a penalty.Overall, with the inclusion of the above changes, we feel that the manuscript has a more policy-relevant discussion, and the analysis is now framed in a way that makes it more relevant to real-world considerations around different policy mechanisms. 3

Reviewer 2
The manuscript titled 'How reliability and carbon prices impact pathways to universal electricity access in Africa' addresses an important and relevant topic.However, there are several areas where the manuscript needs improvement to enhance its clarity and overall quality.
We thank the reviewer for their comment and are glad they believe that it is an important and relevant topic.We have, where possible, addressed the reviewer's comments (see below), and we hope that they agree that it now has enhanced clarity and quality.

4
The title of the manuscript, "How reliability and carbon prices impact pathways to universal electricity access in Africa," does indeed sound like a question.It would be more appropriate to rephrase it into a statement or summary of the study's objective.For example, "Assessing the Impact of Reliability and Carbon Prices on Achieving Universal Electricity Access in Africa." We thank the reviewer for their useful comment.We agree the previous title was unclear in its wording.We have changed the title to: "Reaching Universal Electricity Access in Africa: A Geospatial Analysis of System Reliability and Carbon Price Impacts" 5 One of the primary issues with this manuscript is its lack of coherence and proper organization.The structure of the paper needs to be improved for better readability and comprehension.Introduction: Provide a clear introduction that outlines the importance of the study, its objectives, and the research question.
We have made changes to the Introduction section to emphasise the importance of the study and to detail the objectives and the research questions more clearly.Please see the last paragraph of the introduction for this section, on Pages 3-4: We thank the reviewer for this suggestion.We have added four further references to the literature review (Introduction section) and we hope this gives a broader picture of existing related research, and the context of the study.The Nature Communications formatting guidelines suggest no more than 70 references, so we are limited in adding further detail given that we have also added references to the discussion section.Please see the Introduction Section on Pages 1-3.

8
Methodology: The methods section should be expanded to provide sufficient detail for the work to be reproduced.Explain the data sources, variables, and statistical methods used in the analysis.
We thank the reviewer for this comment.We have gone through the Methods section and enhanced clarity regarding some of the sections that we deemed potentially less clear.See, for example, improved clarity to the section with the subheading "Estimation of baseline population without access".Additionally, three subheadings within the methods have been updated to better reflect the contents and make things clearer for the reader.
Regarding sources of data, within the Methods section, we have a section "Geospatial Data" that details the geospatial datasets used for the analysis.Some of the detailed modelling data inputs, and the detailed model description, are included in the Supplementary Materials due to the formatting restrictions (Methods word limit).Please see the updated Methods section, Pages 14-20, and the Supplementary Materials, which starts on Page 26.
We now feel that all major sources of data, tools used, and methodological choices are sufficiently clear, having compared to other papers in the Nature Communications journal.9 Results: Present the results in a logical sequence and use clear headings and subheadings to guide the reader through the findings.
Visual aids such as tables and figures should be used to enhance understanding.
We thank the reviewer for their suggestion here.To improve clarity, we have updated all the results subheadings to improve readability and flow.They now read as follows to reflect the different things presented: We thank the reviewer for this comment.We have extended the Discussion, adding additional text to all three main sections.We now go into more depth regarding the real-world relevance of the results, focusing especially on the carbon pricing and reliability aspects of the paper, which are the most novel areas it covers.
Please see the updated Discussion section on Pages 12-14.In addition, please refer to the response to comment 2 in this document which provides some further detail regarding the changes to the discussion.
11 Conclusion: The manuscript lacks a conclusion section, which is essential to summarize the key findings and their significance.Provide recommendations for future research or policy implications.
Nature Communications journal formatting guidelines do not permit a conclusion section.Included in the Discussion section we focus on what we feel are the most salient research findings and have included a discussion of both future research suggestions and policy implications.We hope the reviewer feels satisfied that the discussion section covers the points they would hope to see there.
12 References: Ensure that all references are cited correctly and consistently throughout the manuscript.
We thank the reviewer for pointing out these issues and have gone through the references and reference list to ensure everything is properly presented and consistent.
13 In conclusion, while the topic of the manuscript is noteworthy and relevant, it requires significant revisions to improve its overall quality.The authors should focus on enhancing the structure and coherence of the paper, providing sufficient detail in the methods section, and rephrasing the title to make it more declarative.These revisions will enhance the manuscript's readability and impact.I recommend that the authors carefully address the abovementioned issues and consider incorporating the suggestions into their revised manuscript.
schemes, our analysis points to the impact carbon credits may have, depending on the price level and where they are implemented.Our analysis highlights where schemes may be most effective for supporting lower-carbon electricity access." See section S2.4 and Figure S2 in the Supplementary Materials (Pages 27-8)On carbon pricing, we have included examples of carbon pricing schemes, both taxation schemes and carbon credit schemes in the above-referenced discussion section.There is a carbon tax scheme operating in South Africa, with several other countries in SSA considering implementing one.In addition, we give details (Pages 13-14) of two active initiatives that offer carbon credits to low-carbon electricity access projects.This may be an alternative way in which carbon pricing impacts the shares of technologies used: being developed with the help of financing from carbon credits[46].Schemes such as the Carbon Initiative for Development (Ci-Dev) and the D-REC initiative are facilitating carbon finance support for lowcarbon electricity access projects[33, 47].Whilst not directly translatable from this analysis due to the complexities in carbon#CommentResponse crediting